GermanToEnglish conversion fails

I got an email from eservice intended for a switch to the english version, but with different product key and serial number than my german ones. I guess that's probably why the new serial nr. isn't accepted during setup (first I uninstalled the german program). Is there a way to solve this? Btw here's the email from eservice:

the email you received from eservice@paragon-software.com has the new serial number and installation file for your application. You need to download the installer file(s) using the links provided in the email and the serial number.